Ionization type smoke detector

Abstract

An ionization type smoke detector includes a detector body, a printed circuit board on the upper surface of the detector body, an electrode mount on the upper surface of the printed circuit board, an inner electrode securing the electrode mount onto the printed circuit board and which has a radioactive source, an intermediate electrode screwed onto the electrode mount in such a way as to be situated above the inner electrode, and an outer electrode covering the electrode mount, the inner electrode and the intermediate electrode. The outer electrode has a plurality of smoke inlet windows, and is fixed to the upper surface of the printed circuit board by inserting engagement members at the lower end thereof into insertion holes of the printed circuit board. The electrode mount has an FET accommodating section including a first socket, whereas a second socket is formed on the printed circuit board. Electrodes of an FET are connected to the sockets, respectively. The detector also includes a wind shield ring surrounding the outer electrode and fixed to the upper surface of the printed circuit board by hooks extending into second insertion holes of the printed circuit board. Further, a bug screen is interposed between the outer electrode and the wind shield. A shield case abuts the lower surface of the printed circuit board and is fixed to the lower surface thereof and electrically connected to the outer electrode. A protective cover covers these components and has smoke inlet windows.

What is claimed is: 
     
       1. An ionization type smoke detector comprising: a detector body;   a printed circuit board which is arranged on an upper surface of said detector body and which has first, second and third insertion holes;   conductive connection metal members arranged on a lower surface of said detector body;   terminal screws for simultaneously attaching said printed circuit board and said conductive connection metal members to the detector body;   an electrode mount arranged on an upper surface of said printed circuit board;   an inner electrode which secures said electrode mount onto said printed circuit board and which has a radioactive source;   an intermediate electrode which is screwed onto said electrode mount in such a way as to be situated above said inner electrode;   an outer electrode which covers said electrode mount, said inner electrode and said intermediate electrode, which has a plurality of smoke inlet windows, and which is fastened to the upper surface of said printed circuit board by inserting engagement members formed at the lower end thereof into the first insertion holes of said printed circuit board;   a wind shield ring which surrounds said outer electrode, which controls the speed at which air flows into said smoke inlet windows, and which is fastened to the upper surface of said printed circuit board by inserting hooks formed at the lower end thereof into the second insertion holes of said printed circuit board;   a bug screen placed between said outer electrode and said wind shield ring;   a shield case which abuts against a lower surface of said printed circuit board and which is fastened to the lower surface of said printed circuit board and electrically connected to said outer electrode by inserting engagement sections formed at the upper end thereof into the third insertion holes of said printed circuit board; and   a protective cover which covers said printed circuit board, said outer electrode and said wind shield ring, which has a plurality of smoke inlet windows, and which is fastened to the upper surface of said detector body by engaging hooks formed at the lower end thereof with said detector body.   
     
     
       2. A detector according to claim 1 wherein each of said conductive connection members is a blade metal member composed of a fastening section to be fastened to said detector body by one of said terminal screws and a blade section joined to said fastening section. 
     
     
       3. A detector according to claim 1 wherein said inner electrode includes a radioactive source installing section for installing a radioactive source, and a leg section joined to said radioactive source installing section and having a threaded portion on the peripheral surface at its tip, the leg section being passed through fourth insertion holes formed in said electrode mount and through said printed circuit board to be threadedly fastened on the lower surface of said printed circuit board. 
     
     
       4. A detector according to claim 3 wherein said radiation source installing section has a polygonal configuration. 
     
     
       5. A detector according to claim 1 wherein said printed circuit board has a check terminal for checking a circuit formed thereon. 
     
     
       6. A detector according to claim 5 wherein said protective cover has an insertion hole which is formed at a position corresponding to the check terminal of said printed circuit board, whereby a check bar is insertable through the insertion hole so as to effect a connection to said check terminal. 
     
     
       7. A detector according to claim 1 wherein said printed circuit board is fastened to said detector body by means of said terminal screws at positions on the outside of said wind shield ring. 
     
     
       8. An ionization type smoke detector comprising: an electrode mount which has on its upper surface an inner electrode accommodating section having an insertion hole at the center thereof, said electrode mount further having on its lower surface a plurality of protrusions for temporary fastening;   an intermediate electrode fastened to the upper section of said electrode mount and having at its center a radiation transmission hole;   a printed circuit board having a first insertion hole formed at a position corresponding to the insertion hole of said electrode mount and a plurality of second insertion holes through which the plurality of protrusions of said electrode mount are inserted., respectively;   an inner electrode having a polygonal radioactive-source installing section and a leg section joined to said radioactive-source installing section, said leg section having a threaded portion at a free end thereof, said radioactive-source installing section being accommodated in said inner electrode accommodating section of said electrode mount, the leg section passing through the insertion hole of said electrode mount and the first insertion hole of said printed circuit board;   a radioactive source disposed on an upper surface of said radioactive-source installing section;   a threaded fastener threaded to said threaded portion of the leg section of said inner electrode at the lower surface of said printed circuit board to secure said inner electrode to said printed circuit board; and   an outer electrode which covers said electrode mount, said inner electrode, and the intermediate electrode and which is fastened to said printed circuit board.   
     
     
       9. A detector according to claim 8 wherein said electrode mount has a cylindrical wall formed in the periphery of said inner electrode accommodating section. 
     
     
       10. A detector according to claim 9 wherein the cylindrical wall has in its edge portion an FET accommodating section and at least one screw hole for mounting the intermediate electrode, and which FET accommodating section and at least one screw hole are circumferentially spaced apart from each other along said cylindrical wall. 
     
     
       11. A detector according to claim 10 wherein said FET accommodating section has an open lower end portion and an upper surface equipped with a connection terminal connected to a terminal of said FET. 
     
     
       12. A detector according to claim 8 wherein said printed circuit board has on its upper surface a shield section, a check terminal for checking a circuit, and an electrode mount installing section. 
     
     
       13. A detector according to claim 8 wherein said inner electrode has a radioactive-source protection cover for securing in position the radioactive source placed on the radioactive-source installing section. 
     
     
       14. An ionization type smoke detector comprising: a printed circuit board;   an electrode mount arranged on said printed circuit board and having an FET accommodating section for accommodating an FET;   an inner electrode which is attached to said electrode mount and to which a radioactive source is fastened;   an intermediate electrode fastened to an upper section of said electrode mount;   an outer electrode which covers said electrode mount, said inner electrode and the intermediate electrode and which is fastened to said printed circuit board;   a first socket formed in the FET accommodating section of said electrode mount and electrically connected to the intermediate electrode;   a second socket formed on said printed circuit board; and   an FET which is accommodated in the FET accommodating section of said electrode mount and whose electrodes formed at its ends are respectively connected to the first and second sockets.   
     
     
       15. A detector according to claim 14 wherein that portion of said FET accommodating section of said electrode mount which abuts on said printed circuit board is formed as an open section, which is closed by said printed circuit board. 
     
     
       16. A detector according to claim 14 wherein the first socket is connected to the gate electrode of said FET and the second socket is connected to the drain and source electrodes of said FET. 
     
     
       17. A detector according to claim 14 wherein said printed circuit board includes a first board on which various circuit parts are mounted and to which said electrode mount is attached, and a second board provided with a second socket and soldered to the first board. 
     
     
       18. A detector according to claim 14 wherein said printed circuit has a shield section which occupies the greater part of its surface, said FET being shielded by the shield section of said printed circuit board and said outer electrode. 
     
     
       19. A detector according to claim 14 further comprising a connection terminal provided on said electrode mount and having one end electrically connected to the first socket and the other end protruding upwardly beyond said electrode mount, said intermediate electrode having a spring hole for holding the other end of said connection terminal, electrical connection between the first socket and said intermediate electrode being achieved by fitting the connection terminal into the spring hole of the intermediate electrode. 
     
     
       20. A detector according to claim 19 wherein one end of the connection terminal extends through said electrode mount so as to face the interior of said FET accommodating section, the first socket being connected to that one end. 
     
     
       21. A detector according to claim 14 wherein said electrode mount has projections formed on its upper surface, said intermediate electrode having insertion holes through which the projections of said electrode mount are inserted. 
     
     
       22. An ionization type smoke detector comprising: a printed circuit board having a printed circuit formed on a lower surface thereof, a plurality of first insertion holes, and a second insertion hole;   an electrode mount arranged on an upper surface of said printed circuit board;   an inner electrode which is mounted on said electrode mount and to which a radioactive source is fastened;   an intermediate electrode fastened to an upper section of said electrode mount;   an outer electrode which is fastened to the upper surface of said printed circuit board in such a way as to cover said electrode mount, said inner electrode and the intermediate electrode and which has a plurality of smoke inlet windows formed in a side wall thereof,   said outer electrode having a plurality of engagement sections, which are formed at its lower end, abutting said printed circuit board and which are inserted through the first insertion holes of said printed circuit board said engagement sections being secured by solder to said printed circuit on the lower surface of said printed circuit board, and an engagement hole in its side wall; and   a shield case abutting the lower surface of said printed circuit board and electrically connected to said outer electrode, the shield case having an engagement section formed on its upper end section and which is received in the insertion hole of said outer electrode in engagement with said outer electrodes, said engagement section passing through said second insertion hole of said printed circuit board.   
     
     
       23. An ionization type smoke detector comprising: a printed circuit board in which a plurality of first insertion holes are formed;   an electrode mount arranged on an upper surface of said printed circuit board;   an inner electrode which is attached to said electrode mount and to which a radioactive source is fastened;   an intermediate electrode fastened to an upper section of said electrode mount;   an outer electrode which is fastened to the upper surface of said printed circuit board in such a way as to cover said electrode mount, said inner electrode and the intermediate electrode and which has a plurality of smoke inlet windows formed in a side wall thereof; and   a wind shield ring which surrounds said outer electrode, which has a speed reduction mechanism for airflow through the smoke inlet windows of said outer electrode, and which is fastened to the upper surface of said printed circuit board by inserting hooks formed at the lower end thereof through the first insertion holes of said printed circuit board.   
     
     
       24. A detector according to claim 23 wherein said outer electrode includes a small-diameter cylindrical section whose upper end is closed and which has a plurality of smoke inlet windows formed in a side wall thereof, and a large-diameter cylindrical section which is connected to the lower end of the small-diameter cylindrical section, which has a diameter larger than that of the small-diameter cylindrical section, and which has an open lower end section abutting on the upper surface of said printed circuit board. 
     
     
       25. A detector according to claim 24 wherein said outer electrode has a plurality of engagement sections formed at the lower end of the large-diameter cylindrical section and is fastened to the upper surface of said printed circuit board by inserting these engagement sections into second insertion holes of said printed circuit board. 
     
     
       26. A detector according to claim 24 wherein said wind shield ring consists of a cylindrical member having substantially the same height as said outer electrode and a size which enables it to accommodate said outer electrode. 
     
     
       27. A detector according to claim 26 wherein said wind shield ring includes a large-diameter cylinder situated on the outside of the large-diameter cylindrical section of said outer electrode, a small-diameter cylinder situated on the outside of the small-diameter cylindrical section of said outer electrode, an annular step section joining the small-diameter cylinder to the large-diameter cylinder; and an airflow-speed-reduction mechanism formed on an upper section of the small-diameter cylinder. 
     
     
       28. A detector according to claim 27 wherein the airflow-speed-reduction mechanism includes a ring having a diameter smaller than that of the small-diameter cylinder and larger than that of the small-diameter cylindrical section of said outer electrode, and a plurality of struts formed on the upper section of the small-diameter cylinder for the purpose of supporting the ring in an upper inside section of the small-diameter cylinder. 
     
     
       29. A detector according to claim 27 wherein an inner wall of the annular step section is substantially in contact with the periphery of said outer electrode. 
     
     
       30. A detector according to claim 27 further comprising a protective cover which covers said printed circuit board, said outer electrode and said wind shield ring and which has a plurality of smoke inlet windows. 
     
     
       31. A detector according to claim 30 wherein an outer wall of the annular step section of said wind shield ring is substantially in contact with an inner wall of the protective cover. 
     
     
       32. A detector according to claim 30 further comprising a bug screen placed between the small-diameter cylindrical section of said outer electrode and the small-diameter cylinder of said wind shield ring.